1995 ranger

[dlmicco]

Recently I expearianced acheck engine light and the scan unit displayed p1131 which is something you all know about. The o2 sensor had been in the exaust for at least 4 years. Its the one prior to the converter. the scanner reads #1 bank, lean burn.I without thought changed the o2 sensor. After about 16 miles on the road the light came back on with the same code. I checked for vacum leaks and found a hose to the PCV valve leaking so I replace the hose and the pcv valve.I also cleaned the MAF sensor believing that it could contribute. I drove the truck for about the same number of miles and sure enough the light is back on again. Could it be possible that the sensor is bad out of the box?? or could I be missingsomething??

 

[RonD]

What engine is in the '95 Ranger?

The O2 sensors can not be used when engine is cold, they need to be above 650degF to operate properly, so they wouldn't set a code until engine was at operating temp, 5 minutes, or so, from cold start.
There is also a timer in the PCM that causes it to ignore O2 sensor input for 60 seconds, or so, after engine is restarted when warm, this allows exhaust pipe(O2 sensor) to heat up again.

They added heaters to O2 sensors to make them more stable and to get them on-line faster for better MPG, it is always good to check the fuse and wiring on O2 sensors.
The O2 sensor only sends out .1v-1.0v, below.5v is lean, above .7v is rich, so any wire issue can effect this minimal voltage.

As a test I would warm up the engine to operating temp.
Turn off engine and reset CEL.
Restart and wait for a minute or two(timer) without driving it, see if CEL comes back on.
If it comes on I would suspect a vacuum leak, idle is highest vacuum.
If not then drive it and see if it comes on.
If it only comes on when driving then it could be injectors or low fuel pressure in the rail.
Pressure should be 32psi-42psi while running, but also do a static test to see if it holds pressure with engine off.
Low fuel pressure could only effect one bank if its a small drop.
I would run some seafoam in the tank to clean up injectors.

Most fuel injected engines Bank Fire the injectors, so on a V6 3 injectors fire at the same time, this keeps the intake full of fuel vapor.
On the 4.0/3.0 engines injectors are fired 123 at the same time then 456 at the same time.
If one injector is not allowing enough fuel out then that could also effect only 1 bank.


And yes it could just be a bad new O2 sensor, new doesn't mean "it works" anymore, new now means "never tested", lol.